1. Field of the Invention
The invention relates to a temperature control apparatus for an ink jet printer and, more particularly, to a temperature control apparatus which utilizes a heater for heating the pressurized ink in a ink jet printer utilizing an ink recycling system.
2. Brief Description of the Prior Art
Various ink jet printing systems are well known in the art. It has been considered desirable to recycle the unused or waste ink. However, a well known difficulty has risen in connection with recycling the ink. Because of the evaporation of the solvent of the ink during the transit of the ink between the nozzle, and the drain or gutter of the ink jet printer, the viscosity of the ink is subject to variation. The ink is exposed to the ambient air while in transit between the nozzle and the drain.
Ink jet printers have been developed for making a record on a writing medium by generating a series of ink drops, applying a charge successively on each of these ink drops in response to a received signal, and then directing these ink drops along a path between two parallel conductive plates. A bias potential is applied to these plates with the result that the ink drops are deflected so that when they reach the writing medium (or material upon which it is desired to write) they provide a representation of the information contained in the signals. The general configuration employed for ink drop printers consists of an ink sump which contains ink. The sump feeds a pump which in turn feeds a conduit which is connected to a nozzle. An electromechanical transducer is employed to vibrate the nozzle at some suitably high frequency which causes the ink to be ejected from the nozzle in a stream which shortly thereafter breaks into individual drops. It is desirable for proper charging of the individual drops that the breakup of the stream occurs within the charging slot which is the location along the path where the actual charging of each individual drop takes place.
It is well known in the art that the viscosity of the ink or writing fluid is one of the major parameters which determines the location along the path of the stream of ink where the breakup into individual drops occurs. A change in the viscosity of the ink or writing fluid will cause the point at which breakup occurs to change which in turn effects the charging of the ink drops in response to the signal. It is further well known that viscosity of fluids varies with temperature and, in the case of some inks and other fluids, extremely rapidly. The design parameters of ink jet printers generally allow for some variation in the viscosity of the fluid but with the addition of an ink recycling system it has been found to be desirable to gain greater control over the viscosity of the fluid by maintaining a stable temperature for the ink entering the nozzle. This temperature related phenomenon is observed where the characteristics of individual nozzles vary with the temperature of the operating environment. The greater variation in the viscosity experienced with ink recycling systems is due to evaporation of the solvent component of the ink (as discussed above). It is anticipated that other applications of the temperature control apparatus within the ink jet printer described herein will be found wherever there is a need to gain additional control over the viscosity of the ink or writing fluid being utilized in the system.